NEW YORK (AP) — Determined to mobilize midterm Democratic voters, President Barack Obama is issuing an election-year warning against state voting requirements and early balloting restrictions that many in his party fear will curb turnout in an already difficult year for Democrats.

A day after hailing the Civil Rights Act as a lasting legacy of Lyndon B. Johnson's presidency, Obama is using another civil rights forum to draw attention to the Voting Rights Act and take issue with Republican measures in some states that Democrats say are eroding the landmark 1965 law that helped pave Obama's path in politics.

Obama's Friday address to civil rights activist and television talk host Al Sharpton's National Action Network conference in New York is part of the administration's effort to motivate voters and push back against state voting restrictions prompted by last year's Supreme Court invalidation of a key provision of the Voting Rights Act.

For the remainder of the year, no political issue stands out more prominently for Democrats than their ability to motivate voters to turn out at the polls in November. Control of the Senate, now in the hands of Democrats, is at stake, as is Obama's already limited ability to push his agenda through Congress.

But traditionally weak midterm turnout by Democrats coupled with efforts in some states to limit early voting and to enact voter identification requirements have prompted the president and his party to raise alarms and step up their get-out-the-vote efforts.

Republicans have long argued that identification requirements and other voting controls are reasonable measures designed to safeguard the balloting process, not to suppress voter turnout. Democrats say photo identification requirements especially affect minority or low-income voters who may not drive and thus wouldn't have an official government ID.

Obama previewed that sentiment earlier this week while raising money for Democrats in Houston: "the idea that you'd purposely try to prevent people from voting."

When one donor shouted out that the Republican effort was "un-American," the president promptly concurred. "Un-American. How is it that we're putting up with that?"

Obama's speech Friday comes a day after he marked the 50th anniversary of the Civil Rights Act at the LBJ Library in Austin, Texas, where he praised Johnson's understanding of presidential power and his use of it to create new opportunities for millions of Americans.

Just last year, seven states passed voter restrictions, ranging from reductions in early voting periods to identification requirements, according to the Brennan Center for Justice at New York University School of Law. North Carolina alone adopted a photo ID requirement, eliminated registrations on Election Day and reduced the number of early voting days. Overall 34 states have passed laws requiring voters to show some form of identification at the polls.

The North Carolina steps, which take effect in the 2016 election, came after the Supreme Court last June threw out the crucial section of the Voting Rights Act that required that all or parts of 15 states with a history of discrimination in voting, mainly in the South, get federal approval before changing their election laws.

Bipartisan legislation proposed in the House and Senate would attempt to address the constitutional concerns raised by the Supreme Court. But sponsors such as Sen. Pat Leahy, D-Vt., and Rep. James Sensenbrenner, R-Wis., are still trying to line up enough support for the proposals.

The proposed bill would require four states — Georgia, Louisiana, Mississippi and Texas —to get approval from the Justice Department before making any changes in the way they hold elections. In an effort to secure Republican votes, it provides an exception for states that want to adopt photo identification requirements.

Offering a potential compromise, former United Nations Ambassador Andrew Young, once a top aide to Martin Luther King Jr., suggested during his own remarks at the LBJ Library this week that Obama use his executive power to require optional photos on Social Security cards as a remedy for states that impose voter ID laws.

Meanwhile, the administration is stepping up its offensive. Attorney General Eric Holder has challenged the North Carolina election law as well as one in Texas.

Vice President Joe Biden added his weight to the issue this week with a video for the Democratic National Committee denouncing the voter restrictions.